First things first: have you checked with your land lord?
What is the construction of the wall, ie: wallboard on studs or masonry, is it a curtain wall or load bearing?
What is the total weight of your scrap metal and what is the are you plan to mount it in?
If the individual pieces are over 10# or so, gluing might not be the way to go. Mounting on canvas would not be the optimum way as the if the glue lasts, the canvas under the strain will not, it will at least start to sag.